Aliphatic polyesters, an important class of technologically important biodegradable and/or biocompatible polymers, are readily accessible via chemical synthesis by ring-opening polymerization (ROP) of cyclic esters or lactones with relatively high strain energy. The five-membered γ-butyrolactone (γ-BL) would be a desirable bio-derived monomer for the chemical synthesis of the biopolyester poly(γ-butyrolactone) (PγBL), as γ-BL is a key downstream chemical of succinic acid that was recently ranked first in Department of Energy's top 12 biomass-derived compounds best suited to replace petroleum-derived chemicals. However, γ-BL, due to its low strain energy, is commonly referred as “non-polymerizable” in textbooks and literature (see, for example, Houk et al., Why δ-valerolactone polymerizes and γ-butyrolactone does not. J. Org. Chem. 73, 2674-2678 (2008)). Lipase-catalyzed ROP of γ-BL yielded a mixture of oligomers (˜11-mer), while high molecular weight (MW) microbial poly(4-hydroxybutyrate) (P4HB), a structural equivalent of PγBL, which has been shown to exhibit more desired properties as a biomaterial (e.g., faster degradation rates and better mechanical properties) relative to other commonly used aliphatic polyesters, is produced through a bacterial fermentation process. Chemical ROP process has only been realized under ultra-high pressure (e.g., 20,000 atm) and high temperature, producing only oligomers.
Accordingly, there is a need for and techniques for polymerizing five-membered butyrolactones and substituted versions thereof without the need for significant temperature or pressure. There is also a need to identify catalysts for these techniques, a need for the novel polymers of the polymerizations, and a need for copolymers of the resulting products that are biodegradable and recyclable.